Thermal Desorption and Photoelectron Spectroscopy of NO Adsorbed on ZnO(1010)

Exposure of the ZnO(1010) prism face to NO at 90 K leads to two molecularly adsorbed NO species. The weakly bound form desorbs at 110 K and the strongly bound form desorbs at 420 K for low exposure and at 300 to 450 K for high exposures. Adsorption of the strongly bound form is activated and slower than of the weakly bound NO. Simultaneously, NO reacts partly to N2O at 90 K. N2O desorbs at 140 K, oxygen desorption is not observed and it is concluded that the oxygen formed during the NO to N2O conversion diffuses into the substrate. After annealing to 190 K, the weakly bound NO and N2O desorb. After several cycles of reexposing and annealing to 190 K, N2O formation is completely suppressed due to accumulation of either oxygen or the strongly bound form of NO or both. The strongly bound NO increases, the weakly bound NO decreases the electron affinity χ. After saturation with the strongly bound form, the final increase of χ amounts to 1.2 eV.